412 METALLURGY OP IRON AND STEEL.
caused considerable stir, and yet in 1903 there was not a single converter of this type at work in America. Of the Boberts-Bessemer plants only two were active in that year. There were eight Tro-penas plants at work, one Bookwalter converter and two vessels of special design. All these plants were making steel castings. The open-hearth furnace is the recognized agent for the making of steel, castings. It allows control both of the composition of the metal and of the casting conditions. Most furnaces used for castings have an acid lining, but sometimes the hearth is basic. In the latter case there are more troubles'and a somewhat greater working cost, but there is an advantage in the ability to use a poorer quality of scrap. Basic metal is more lively, and there is greater danger of honeycombs, but such metal is used to some extent in this country and quite extensively abroad, and it is economy to use the basic process when high-phosphorus scrap can be bought much cheaper than the selected stock called for by the acid hearth. It is currently supposed that the open-hearth furnace cannot make steel hot enough for small castings. This is a mistake, as in a proper furnace almost any desired temperature can be reached, and care must be taken to keep the metal from becoming too hot.
SEC. XXc.—Slow-holes.—The use of good stock determines to a great extent the nature of the product, but does not influence the solidity of the eastings. This depends partly on the temperature and composition of slag and metal before tapping, and partly on the quantity and nature of the recarburizing additions. An increase in these latter agents covers up errors in manipulation, but shows itself in a higher content of metalloids. Honeycombed metal may arise from bad casting conditions or from a laudable desire to reduce the proportions of silicon and. manganese, for the blowholes decrease only slightly the strength and toughness of a casting, while the complete removal of them by overdoses of metalloids gives a brittle metal.
It is the current impression that all the difficulties in making sound castings have been overcome by the introduction of metallic aluminum and certain alloys of silicon. Great progress has been made, but there is no magic wand for sale which can be waved over a ladleful of steel to "kill" it "dead." Hadfield* says: "There is no rapid or royal road to the production of sound steel castings; this
* Aluminum. Steel. JournalL and S. I., Vol. II, 1890, p. 174.